An internal combustion engine, such as those used in marine outboard engines, is powered by the combustion of fuel in one or more cylinders. During the operation of such an engine, the heat generated by the combustion of fuel in the cylinders must be dissipated to prevent overheating of the engine and consequent damage to engine components. Other components of the engine, such as fuel system, exhaust pathways, and electronics, can also experience an increase in temperature during use and require cooling to maintain normal operation.
One common method of providing cooling in marine applications is with an open loop cooling system. Water is pumped from the body of water in which the engine is operating, for example using a pump driven by either the crankshaft or the driveshaft of the engine. Referring to FIGS. 1A and 1B, one commonly used type of pump is a hybrid pump 10 that combines attributes of a centrifugal pump and a positive displacement pump. The pump 10 involves a flexible impeller 12 eccentrically mounted inside a housing 14. At low speeds (FIG. 1A), the impeller 12 is in contact with the housing 14 and the pump 10 acts as a positive displacement pump. At high speeds (FIG. 1B), the impeller 12 flexes away from the housing 14 and the pump 10 acts as a centrifugal pump. As a result, this pump design provides a flow of water over a wide range of rotational speeds, but with lower efficiency than either a displacement pump at low speeds or a centrifugal pump at high speeds. The water is pumped to one or more components that require cooling, such as a water jacket of the engine, an exhaust manifold and electronic components. The water is then returned to the body of water.
While this arrangement is adequate for cooling the engine, it has some drawbacks. The water drawn in by the pump 10 may contain salt or debris that can damage the impeller 12, for example by getting caught between the impeller 12 and the housing 14 and causing wear on the impeller 12, resulting in reduced flow of cooling water or even failure of the pump, potentially damaging the engine. In the event of damage to the pump 10, the pump is often difficult to access and service because it is typically located above the cavitation plate of the engine so that it can be conveniently driven by the crankshaft or driveshaft. In addition, while the pump 10 is operational at all speeds, it may not provide a sufficient flow of water for adequate cooling, particularly at very low speeds when the speed of the pump 10 may not be sufficient to deliver the required volume of cooling water, and at very high speeds when the pump 10 experiences reduced efficiency. One alternative design, a centrifugal pump, is less susceptible to wear but provides insufficient cooling at low speeds.
Therefore, there is a need for a method of providing improved cooling to a marine engine over a wide range of engine speeds.
There is also a need for a marine engine having improved cooling over a wide range of engine speeds.
There is also a need for a pump assembly requiring low maintenance and being easy to service and repair.